Future upcoming technologies and what audit needs to address

Transcription

1 Future upcoming technologies and what audit needs to address Dr R.I MacKay

2 History of audit Absolute dose - Simple phantom standard dose measurement Point doses in beams - Phantoms of relatively simple geometry - Several points in beam Treatment simulation - Point doses - Semi anatomical phantom - Realistic treatment technique - Scan Plan - Treat IMRT - Absolute dose and dose distribution - More complex treatment protocol Rotational Audit - Challenging geometry - Test of planning system and dose delivery Advanced techniques - SABR

3 Advanced Radiotherapy Modality Small field High Intensity Modulation Adaptive Radiotherapy Imaging High dose rate Gating/Trac king Protons? Flattening Filter Free VMAT Cyber Knife Tomotherapy SRS Linac MR linac

4 Challenges in new technology Technology is making dose delivery more diverse New technology is a combination of advanced delivery techniques Audit is traditionally quite rigid - We design the audit for the technique Does this fit our model of regional audit - Collaborative approaches between those with similar technology Can we make the measurement system more flexible

5 Model Anatomy for Radiotherapy Verification and Audit In the Head and Neck Average geometry from patient CT scans (4 male, 4 female): - Body - Mandible - Sinuses - Spinal cord (location only) Marvin: Overview Mandible and cavity can be swapped for ABS versions to make a homogeneous phantom

6 Marvin: Detector module Cylindrical detector module - Location maximises coverage of typical PTV locations and spinal cord - Can be designed for any type of detector (film, gel, diode array ) Prototype module designed for pinpoint ionisation chamber - Absolute dose measurements Simple chamber positioning system - 15 chamber holes from centre to edge - Module rotates to 12 fixed positions - Depth of chamber set using spacer rods Chamber can be positioned almost anywhere within the cylinder

7 Chamber positioning code Need to be able to position chamber: - Within the PTV or spinal cord - Avoid steep dose gradients Detector module has >1500 possible chamber positions - Selecting suitable points manually can be difficult Software automates point selection - PTV located as a percentage of the max dose point (typically 90 or 95 %) - Cord position known from average cord geometry - Chamber positions lying within these regions and with low dose gradients identified - Code currently based on Pinnacle file format

8 Example audit results

9 2D DGRT VMAT verification Phantom Free Audit? 3D DGRT Dose reconstruction 2D DGRT Trend analysis

10 Delineation variation: CT versus CT + PET CT (T2N2) SD 7.5 mm CT + PET (T2N1) SD 3.5 mm Steenbakkers et al, IJROBP 2005

11 Potential uses of PET in RT planning 1. Improved diagnosis and staging of disease - Improved sensitivity and specificity of FDG-PET - Can detect distant metastasis and advanced disease - Gregoire et al, J Nuc Med 48(1)S, 2007

12 Potential uses of PET in RT planning 2. Tumour delineation Tumour boundary Involved lymph nodes (10-25%)

13 Potential uses of PET in RT planning 3. Dose modulation Targeted conformal high dose Isotoxic dose escalation Improved local control with no increase in toxicity? 4. Prediction / monitoring treatment response

14 Transfer of Information PET-CT Planning CT Radiotherapy Treatment Clinical Oncologist RT Planning Radiologis t Nuclear Medicine

15 Site Approval

16 Protons Uncertainties in proton therapy are greater - Uncertainty in proton stopping power - Inhomogeneities - Set up uncertainties have a greater effect - Changes in patient anatomy Dose delivery for scanned beams is highly intensity modulated using very small delivery fields -Motion is a well known problem in scanning proton therapy Dose delivery for IMPT is not in itself robust Require dosimetry for protons at same level of photons

17 Audit for proton therapy

18 Validation (4D dosimetry) Introducing Oscar a 4D, anthropomorphic phantom Zakova et al, P142, PTCOG 52

19 Validation (4D dosimetry) 4D CT of Oscar Zakova et al, P142, PTCOG 52

20 Validation (4D dosimetry) Oscar has been irradiated 45s irradiation with protons (Gantry 1) Proton beam Oscar Zakova et al, P142, PTCOG 52

21 Where will it end?

22 Summary Dosimetric audit is a powerful tool and has served radiotherapy well Treatment techniques become more diverse as technology progresses and audit must become more flexible Greater collaboration between users of particular delivery systems Need to extend the audit process to include additional information that will increasingly affect how we deliver radiotherapy - Particularly functional imaging Require dosimetry for protons at same level of photons. - New tools for audit required